In large bowl, with electric mixer on medium speed, beat butter and sugar until light and fluffy. Add egg and vanilla and beat until blended. Add melted chocolate and continue mixing until blended, scraping side of bowl as necessary. Reduce mixer speed to low and add flour mixture; beat until blended and dough forms.

Spoon dough into pastry bag fitted with a #3 star tip. On greased baking sheets, pipe dough in spirals to make 4-inch round cookies that are 1 1/2 inches apart.

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